Computed tomography (CT) is a medical imaging technique that produces three-dimensional images of internal human body parts from a large series of two-dimensional X-ray images (called profiles) taken in a single-axis rotating structure called a gantry. When compared to a conventional X-ray radiograph, which is an image of many planes superimposed on each other, a CT image exhibits significantly improved contrast.
With the advent of diagnostic imaging systems like CT, where complex and intensive image processing is required, semiconductors play a very important role in developing systems with increased density, flexibility and high performance. The helical or spiral CT machines that use faster computer systems and optimized software can continuously process the cross-section images while the object passes through the gantry at a constant speed.
X-ray slice data is generated using an X-ray source that rotates around the object, with X-ray detectors positioned on the opposite side of the circle from the X-ray source. Many data scans are taken progressively as the patient/object is gradually passed through the gantry. A scintillator receives x-rays attenuated by the patient and generates light. A data acquisition system includes a plurality of detectors or channels.
A detector receives the light form the scintillator and generates a corresponding current signal which is further converted to a digital signal. Since, the x-rays emitted by the x-ray source undergo attenuation while passing through the patient, not all the detectors of the plurality of detectors receive a large signal. Most of the detectors receive a very small attenuated signal (less than 10-15% of the signal emitted by the x-ray source).
Traditional, data acquisition systems provide a fixed gain for all the detectors of the plurality of detectors. This causes noise to be high for all the channels, and even for those channels which receive the very small attenuated signal.